1. Field of the Invention
This invention relates generally to flow control valves. More specifically, it concerns a liquid flow regulator that blocks or controls the flow therethrough at precise discharge rates, suitable for intravenous infusion systems.
2. Description of the Prior Art
Medical treatment may require intravenous infusion of liquids into a patient's blood system for replacing blood, providing food energy, correcting acidity, or introducing drugs. The rate of introduction of the liquid must be carefully controlled for the health or safety of the patient. Pinch clamps acting directly upon a conduit made of plastic tubing have been used to control liquid flow within the conduit. Such clamps have been unreliable and require frequent attention to maintain proper adjustment. Various flow control devices have been developed to provide a more uniform flow rate.
U.S. Pat. No. 3,880,401, issued Apr. 29, 1975 to Harold L. Wiltse, shows a combined flow metering and shut-off valve. Inner and outer valve parts are axially movable relative to one another to effect relative axial movement of a metering valve plug on one part into and from a metering bore in the other part for regulating and blocking flow through the valve passage. A tapered groove portion on the valve plug forms with the wall of the metering bore a flow passage whose effective cross-sectional flow area increases as the plug retracts and decreases as the plug enters the bore.
U.S. Pat. No. 4,223,813, issued Sept. 23, 1980 to Scott T. Garrett et al., discloses a fluid-flow limiting device having a rigid plastic part and a stretchable elastomeric membrane that together define a metering chamber with an inlet and an outlet. A plastic section fuses to the rigid plastic part and the membrane is enveloped between the part and section. Movable valve members fit through openings in the section to the membrane to stretch it and close off the inlet or the outlet, as appropriate.
U.S. Pat. No. 4,300,552, issued Nov. 17, 1981 to Raymond E. Cannon, shows an intravenous flow control apparatus having a button with V-shaped notches. A flexible diaphragm is positioned above the notches and can be forced against the button and partially into the notches by a pusher rod so as to control the rate at which fluid flows through the notches from an input line to an output line.
U.S. Pat. No. 3,058,431 to Eddy discloses a valve which utilizes a tubular valve head of rubber or rubberlike material and which can be expanded outwardly by a longitudinally movable sphere extending within the valve head to block flow through the narrow cylindrical passageway surrounding the valve head.
U.S. Pat. No. 3,985,336 to Bentley discloses a drip irrigation valve including a tubular outer member having a longitudinally extending groove along its inner wall of continuously variable cross-sectional area. An inner member is axially movable within the outer member and includes a resilient O-ring which engages the wall of the outer member at the groove to close off flow through the valve except through the groove passageway at the O-ring. By axially shifting the position of the inner member relative to the groove the flow rate is controlled.
U.S. Pat. No. 3,851,668 to Benjamin discloses a flow control device which operates by moving a rigid ball axially within a flexible tube having channels of varying lengths provide in the interior wall of the tube for passing the liquid flow past the ball.
Other patents showing flow control devices for intravenous systems include U.S. Pat. No. 2,771,878, issued Nov. 27, 1956 to W. E. Folland et al.; U.S. Pat. No. 3,460,526, issued Aug. 12, 1969 to R. W. McKirdy et al,; U.S. Pat. No. 3,620,500, issued Nov. 16, 1971; and U.S. Pat. No. 3,841,354, issued Oct. 15, 1974 to Roy Edward McDonnell.